The present invention relates to aluminum alloy line formed in an LSI and, more particularly, to an improved aluminum alloy line formed by microminiaturization, having a small number of defects (referred to hereinafter as "Al void").
The achieving of high integration in semiconductor integrated circuits has recently become highly desirable. High integration requires the use of specialized techniques for microminiaturization and multi-metal-layer lamination in a line structure. Microminiaturization of the line structure necessitates the design of an aluminum alloy line of much narrower width than has previously been attained. When the width of the aluminum alloy line is reduced to as small as 2 to 3 microns or less, Al voids tend to occur in the line.
Since the multi-metal-layer line structure is made of various thin films such as thin insulator films and thin aluminum alloy films, stress is imposed on the internal structure of a semiconductor device including the multi-metal-layer line, which causes Al voids to be produced in the aluminum alloy line. A semiconductor integrated circuit having large Al voids is not reliable. For example, Al voids cause the line to burn out or become disconnected, or cause a reduction of its sectional area, resulting in an increase in the electrical resistance of the layer. An increase in the electrical resistance causes increased heat generation which causes the line to become disconnected and thus, the operating speed of the circuit is reduced. The increase in the electrical resistance of the line may cause electromigration when a large current flows in the line.
By means of a model test, it has been found that Al voids are formed in the following way. When tensile stress is applied from a passivation film to the aluminum alloy line, it is concentratedly applied at the crystal grain boundaries of the line. In order to alleviate this concentrated stress, the aluminum atoms moves from the grain boundaries, inevitably forming Al voids. This phenomenon is known as stress migration. Hence, in order to suppress such movement of aluminum atoms, thereby to avoid Al voids, copper, which can readily precipitate in the grain boundaries an in Al-Si allow line, has been added to the allow, thus providing an Al-Si-Cu alloy line. In the Al-Si-Cu alloy line, the copper acts as an obstacle to the movement of the aluminum atoms, thus suppressing the formations of Al voids.
However, while the Al-Si-Cu alloy line can suppress the forming of Al voids to a certain degree, it cannot, however, reduce the void coefficient ratio lv of the alloy line below 30%-40%.
Here, the void coefficient ratio lv is the value represented by the following equation: EQU lv=d/W
where W is the width of aluminum alloy line 50, and d is the maximum void width in FIG. 11. The smaller the void coefficient ratio lv the more the occurrence of voids is suppressed.